1. Field of the Invention
The invention relates generally to communications systems. More specifically, the invention relates to peripheral computer connection.
2. Description of the Related Art
Computer peripheral devices, such as modems, can be connected to computers in a wide variety of connection types. Two such connection types in vogue currently are the serial interface type and the PCMCIA (Personal Computer Memory Card International Association) (also known as the PC Card standard) type. The serial interface type can use a port, such that the peripheral can be connected externally to the computer, while PCMCIA uses a PCMCIA slot, requiring connection on that PCMCIA slot.
FIG. 1A shows a prior art external serial modem 110 connected via serial cable 120 to a personal computer (PC) 100. Both external serial modem 110 and PC 100 have serial adapters/ports 114 and 104, respectively. These serial adapters/ports allow a serial cable to be connected to facilitate the transfer of data. The serial adapters/ports 104 and 114 are shown with a plurality of pin-out and pin-in connections which send and receive serial interface signals. Also shown in expanded form are universal asynchronous receive/transmit (UART) components 106 each coupled respectively to PC 100 and external serial modem 110. FIG. 1B is a detailed illustration of a UART and associated signals.
As shown in FIG. 1B, each UART consists of a block of control registers and a pair of shift registers. When the UARTs 106 and 116 receive data from parallel data bus 105 and 115, respectively, to be transmitted (using TX data signal) over serial adapters/ports 104 and 114, the parallel data is stored serially bit by bit in a shift register TXFIFO (transmit first in-first out). The TXFIFO is a serial register capable of holding N bits. Each consecutive bit is shifted such that the first bit is output from the register first, the second bit output second, and so forth. The serialized data is sent over the TX data pin and out through serial adapters/ports 104 and 114. Data is received through the RX data pin from serial adapters/ports 104, 114 and is shifted into a shift register RXFIFO (receive first in-first out). The RXFIFO shift register is connected to the parallel data bus 115 and 105 such that once the shift register is full, all N bits that are held by the shift register are output over the parallel data bus simultaneously.
Referring back to FIG. 1A, in this manner, the UARTs 106 and 116 are capable of converting serial data received from serial adapters/ports 104 and 114, respectively, into parallel form to be transmitted over parallel data bus 105 and 115, respectively. UARTs 106 are also capable of serializing data received from parallel data bus 105 and 115 for transmission through serial adapters/ports 104, 114 over serial cable 120. The CPU 102 of PC 100 is thus able to communicate with modem processor 112 of external serial modem 110. The essential operation is communication of an "embedded" processor (modem processor 112) with a system processor (CPU 102).
The scenario of FIG. 1A represents standard PC serial communication with an external device such as a serial modem. The parallelism in internal structure of PC 100 and external serial modem 110 allows for a UART to be used in each to serialize parallel data in the same manner. However, the serial interface as currently implemented in the art does not allow a PCMCIA device which typically connects to a PCMCIA slot via a power connector/cable to connect via a serial interface.
FIG. 2 shows a PCMCIA (PC Card) external modem 210 coupled to a PC 200. External modem 210, a PC Card device, also makes use of UART but in a different manner from external serial modem 110. External modem 210 is, essentially, a pair of UARTs 216 and 217. UART 216 is coupled over parallel data bus 215 to a modem processor 212. UART 217 represents the UART of the serial interface on the PC-end, as shown in FIG. 1A, transplanted to the PCMCIA modem. In practical design, the two UARTs are not physically separate entities though so pictured in FIG. 2. PC 200 has card detect circuitry which utilizes pull-up resistors 203 and 201 coupled to each of card detect pins 230 and a NOR gate 204. If modem 210 is connected via PCMCIA connector 220, card detect pins 230 will be active low and after inversion at NOR gate 204 cause the PCMCIA I/F (interface) 206 to recognize that an external device has been plugged in. CPU 202 communicates with modem processor 212 by sending/receiving data on parallel data bus 205 and then through PCMCIA I/F 206.
Currently, PCMCIA or PC Card devices are designed to only operate whilst plugged into the PC. When the devices are removed, their connection to the PC is lost. There is a need in some instances to be able to connect to the PC even though the device is not plugged into the PCMCIA slot, such as in a pager modem. It is desirable for a pager modem, whether connected via the PCMCIA or not, to be able to transfer messages to the PC. However, the current design for pager modems does not allow connection to the computer via serial port. Thus, the modem processor in a PCMCIA device such as pager modem, under current practice, utilizes a PCMCIA slot by necessity. Thus, there is needed a mechanism which allows a PCMCIA device to interface via a serial interface to allow the PCMCIA I/F to be otherwise utilized.